Hi
There are multiple ways to do this
1. Do the asset to asset transfer.. The receiver asset will receive the depreciation based on 50 yrs useful life... Then you post unplanned depreciation into the receiver asset..
2. Another option is Scrap the existing asset and upload the values into the new asset based on their useful life / expired useful life...
There are other options as well.. But one of these should be the easy ones for you
Br. Ajay M